This invention relates to novel copolymers containing structural units derived from olefins, xcex1,xcex2-unsaturated mono- or dicarboxylic acids or derivatives thereof and a hydrophobic moiety that is incorporated into the copolymer chain, as well as to a process for preparing these hydrophobically modified copolymers. These polymers are especially useful as additives in cementitious compositions to enhance their flowability and processability. According to a second aspect, the present invention refers to the use of these copolymers as cement additives and to cementitious compositions comprising the copolymer of the present invention.
Surface-active dispersions are commonly used as additives in cementitious mixtures, for example, in mortar or concrete mixtures in order to enhance their flowability and processability. Well-known dispersions in the art are lignosulfonates, naphthalene- or formaldehyde-condensates. However, lignosulfonates show a non-satisfactory performance and naphthalene- or formaldehyde-condensates have come under environmental pressure since they contain residual toxic amounts of free formaldehyde.
Therefore, synthetic water-soluble acrylate-based superplasticizers have been introduced into the market. Among others, they are particularly produced from styrene/(meth)acrylic acid monomers. Typical products and processes for the preparation of such copolymers are disclosed in U.S. Pat. No. 5,138,004, JP-A 62-187152 (xe2x80x9cCement Additivesxe2x80x9d, Production And Use Of Styrene/(Meth)Acrylic Acid And Styrene/Maleic-Anhydride-Copolymers), GB-A-2 221 673 (Use Of Olefin/xcex1,xcex2Unsaturated Dicarboxylic Acid Copolymers), and JP-A 84-62137 (xe2x80x9cLow Molecular Weight StyrenelMaleic-Anhydride-Copolymersxe2x80x9d).
These polymers have, however, in common that they are of very hydrophilic nature due to their higher level of carboxylic acid groups in the polymer backbone. As a consequence, these polymers are very surface-active and promote an air entrainment into the cement/mortar mixtures. Usually, if no defoamers are added to the mortar, the air content can add up to 15 percent or more. The high air content negatively influences other properties of the hardened cement, such as its mechanical strength. Additionally, defoamers, which are added to reduce the air content, separate from the aqueous polymer solution within a very short time, usually within a couple of days only.
Therefore, and because of other reasons, that is, to enhance the performance of such synthetic polymers, these polymers have been modified.
EP-A-736553 discloses a copolymer composed of at least 3 different structural units a), b) and c). Structural unit a) is derived from an unsaturated dicarboxylic acid derivative or cyclic anhydrides and imides of these dicarboxylic acids. Preferred units are derived from maleic acid derivatives. The structural unit b) is derived from an oxyalkyleneglycol-alkenylether, preferably polyethylene oxide-vinyl ether, and, finally structural unit c) is derived from a monomer selected from a wide range of ethylenically unsaturated monomers. However, in general, oxyalkyleneglycol ethers are difficult to produce and they are obtained in lower yields. Therefore, these polymers are rather expensive. Furthermore, they are susceptible to hydrolysis in acidic environments that may occur during preparation of the polymers.
From DE-A-37 28 786 a copolymer comprising styrenic units and units derived from maleic anhydride esterified with a polyalkylene glycol is known wherein only esterification with polyethylene glycols is explicitly disclosed. The used polyethylene glycols still render the copolymer hydrophilic. It is further disclosed that, due to their surface-activity, these copolymers can be used as emulsifiers to improve dispersibility of cement in water. However, the high surface-activity also leads to an undesired high foam level.
EP-A-306 449 discloses copolymers of styrene and maleic acid half-esters. These copolymers are prepared by copolymerization of maleic anhydride and styrene, followed by esterification of the maleic anhydride units with polyalkylene glycols and subsequent neutralization with sodium hydroxide solution. Due to steric hindrance, a minor portion of the maleic anhydride units remains unreacted. However, according to the teaching of this reference, it is preferred to esterify as many maleic anhydride units as possible, although a 100 percent conversion, as envisaged by the teaching of this reference, is in practice, not possible. The preferred polyalkylene glycol is polyethylene glycol. These copolymers are suitable as emulsifiers and increase the flowability of cementitious compositions. It is also mentioned that these copolymers show a reduced level of air entrainment in comparison to comparable copolymers with a lower molecular weight. However, no data are disclosed to enable verification of this statement.
DE-A-41 42 388 discloses copolymers composed of random units represented by the following formula 
wherein M is hydrogen or the residue of a hydrophobic polyalkylene glycol, for example polypropylene glycol or of a polysiloxane; R is a C2-C6-alkylene residue; R1 is a C1-C20-alkyl, C5-C9-cycloalkyl or a phenyl group; x, y and z are integers of 1 to 100; m is an integer of 1 to 100, and n is an integer of 10 to 100, wherein the ratio of x:(y+z) is from 10:1 to 1:10; the ratio of y:z is from 1:5 to 1:100, and m+n equals 15 to 100.
In a preferred embodiment, R is a C2-C3-alkylene group. These copolymers are useful as emulsifiers and plasticizers in cementitious compositions. It is also described that these copolymers do not have the same air entraining properties as comparable copolymers without providing any data.
DE-A-44 45 569 discloses a similar copolymer for the same purpose wherein the styrene moiety is substituted by a moiety derived from an ethylenically unsaturated monomer selected from a wide range of monomers.
In the preferred embodiments of both German applications, R is preferably ethylene, resulting in a hydrophilic polymer still showing high foam levels.
From WO 97/39037 random styrene-maleic anhydride copolymers are known. In one specific embodiment, these copolymers contain hydrophobic polyalkylene glycol and hydrophilic polyethylene glycol residues bonded to the polymeric backbone via an ester linkage.
EP-A 0 930 321 which constitutes prior art according to Article 54(3) and 54(4) EPC, discloses a copolymer comprising:
a) structural units derived from ethylenically unsaturated hydrocarbons;
b) structural units derived from ethylenically unsaturated monomers selected from monocarboxylic acids as well as salts and amides thereof, dicarboxylic acids as well as salts, amides and half-amides thereof and cyclic anhydrides and imides of dicarboxylic acids and mixtures thereof; and
c) structural units derived from monomers selected from esters of ethylenically unsaturated monocarboxylic acids, half esters of ethylenically unsaturated dicarboxylic acids, allyl ethers and vinyl ethers and mixtures thereof having a substituent R linked to the oxygen atom of either the ester groups or the ether group that is selected from:
(i) polyalkylene oxide groups corresponding to the formula 
xe2x80x83wherein R1 is independently at each occurrence selected from hydrogen and C1-C4 alkyl, R2 is C1-C44 hydrocarbyl, t is 0 or 1 and m is an integer in the range of 5-200, with the proviso that if R2 is C1-C5 alkyl, the polyalkylene oxide group does not contain more than 50 weight percent ethylene oxide moieties, based on the weight of the polyalkylene oxide group; and
(ii) groups corresponding to the formula 
xe2x80x83wherein t is 0 or 1 and Q is a polysiloxane residue;
wherein the molar ratio of units b) to units c) in the copolymer is in the range of 1000:1 to 5:1.
The polymers described in this European Patent Application combine high plasticity of the cementitious composition with a low air entrainment due to the incorporation of certain specified hydrophobic residue wherein already a very low level of hydrophobic residues exhibits a very high efficiency in reducing the foam level of cementitious compositions. Although these copolymers show already a considerable improvement with respect to air entrainment in cementitious compositions, it was discovered that these beneficial properties may deteriorate upon storage of a dispersion containing the plasticizer for longer periods of time.
EP-A-612 702, EP-A-753 488, EP-A-792 850, EP-A-850 894, WO 97/48656, WO 95/16643, DE-A-196 53 524 and EP-A-884 290, the latter constitutes prior art according to Article 54(3) EPC, disclose copolymers composed of polyoxyalkyleneglycol(meth)acrylates and other ethylenically unsaturated monomers as additives for cementitious mixtures to improve flowability and processability. These prior art documents all exemplify polyethyleneglycol monoacrylate as polyalkylene oxide-bearing monomers. The polymers containing these monomers suffer from the disadvantages of polyalkylene oxide chains bonded via ester linkages to the polymer-backbone as discussed above and, due to the hydrophilicity of polyethylene glycol chains, these polymers additionally lead to a considerably high air entrainment into the cementitious composition comprising these additives. Thus, for example according to EP-A-753 488, commercially available defoaming agents, shown in Tables III and IV, are added to control the entrained air to be within a desired level.
U.S. Pat. No. 5,561,206 discloses a fluidity controlling mixture for cementitious compositions comprising as a cement dispersing agent, an aqueous solution of a polymer and a oxyalkylene-based defoaming agent which is either dissolved in the polymer solution or stably dispersed in this solution in particles of no more than 20 xcexcm in diameter. To obtain these stable dispersions of defoaming agent particles (droplets) in the aqueous solution of the polymer, the polymerization of a monomer mixture comprising, in a preferred embodiment, an alkylene glycol mono(meth)acrylate acid ester monomer, a (meth)acrylic acid based monomer and, optionally, a monomer copolymerizable therewith, in the presence of a defoaming agent, is carried out. According to the teaching of U.S. Pat. No. 5,661,206, the important feature is to provide a stable dispersion of defoaming agent in an aqueous solution of a polymer wherein the defoaming agent particles or droplets have a maximum size. From this reference, it is evident that the defoaming agent is not integrated into the polymer backbone and that the reaction conditions are selected such to avoid grafting or incorporation of the defoaming agent into the polymer backbone. Consequently, the cementitious compositions containing the dispersion of this prior art reference also suffer from the problem that low air entrainment cannot be maintained upon longer storage time. This is especially true since in U.S. Pat. No. 5,661,206 a stable dispersion is defined as remaining stable for at least 24 hours, whereas in practice the polymeric additives for cementitious applications are stored for considerably longer periods prior to use.
WO 97/44288, WO 97/47566 and U.S. Pat. No. 5,393,343 all refer to acrylic polymers having polyoxyalkylene chains pendant on the polymer obtained by reacting polyoxyalkylene amines with the carboxyl functionality of either the acrylic polymer that may also contain maleic anhydride units or with the corresponding monomers prior to polymerization resulting in amide or imide bonds. The disclosed polyoxyalkylene chains are primarily composed of ethylene oxide units resulting in a high hydrophilicity of the copolymer. These references are also completely silent with respect to the incorporation of hydrophobic compounds into the polymer backbone.
EP-A-271 435 discloses a composition comprising hydraulic cement and a graft polymer plasticizer. The latter comprises a polyether backbone polymer and 2 to 30 weight percent of side chain vinyl-based polymers prepared by the polymerization of an ethylenically unsaturated monomer, preferably acrylic acid. The polyether is a polyalkylene oxide, preferably a hydroxyl terminated oxyethylene/oxypropylene copolymer. The polymerization is conducted in the presence of a free radical initiator and at a reaction temperature of 100xc2x0 C. to 180xc2x0 C. According to the specification of that reference, the term xe2x80x9cgraft copolymerxe2x80x9d refers to the reaction product mixture that additionally contains by-product materials like non-grafted addition homopolymers, polyether degradation products and unreacted polyether.
Although the cementitious compositions comprising this reaction product show good plasticity, as well as low air entrainment, the process of that prior art reference as well as the products resulting therefrom have some unacceptable drawbacks. The polymers of the prior art contain a very high level of polyether, between 60 and 98 weight percent, based on the weight of the graft copolymer. Additionally, the product is very unspecified since it may contain different types of side-reaction products or unreacted products that may influence the properties of the reaction product that is used as plasticizers for cementitious compositions. As a consequence, the beneficial properties of cement plasticity at low air entrainment can only be achieved if an extremely high level of hydrophobic polyethers is used. These polyethers are very expensive raw materials. Thus, the prior art product can only be produced at an unacceptable high price. Additionally, the preparation process described in EP-A-271435 requires very high temperatures that may result in decomposition as mentioned in the specification, and in a more complicated process handling.
Thus, the objective of the present invention is to provide a new process for preparation of a plasticizer for cementitious compositions that avoids the above-described drawbacks, especially with respect to process handling and economy. It is a further objective of the present invention to provide a plasticizer for cementitious compositions showing improved plasticity as well as low air entrainment wherein these beneficial properties are not significantly reduced upon longer storage times of the plasticizer in aqueous solution or dispersion. It is a further objective of the present invention to provide a product having the above-defined benefits at low production costs.
Surprisingly, these different objectives have been attained by a process for the preparation of a copolymer containing structural units derived from xcex1,xcex2-unsaturated mono- or dicarboxylic acids and their salts, half-esters of dicarboxylic acids or salts thereof, an olefin and a hydrophobic moiety, said hydrophobic moiety being incorporated into the copolymer chain; said process comprises reacting in an aqueous medium
a) at least one monomer selected from xcex1,xcex2-unsaturated mono-carboxylic acids and their salts; and xcex1,xcex2-unsaturated dicarboxylic acids, their half-esters free of polyalkylene oxide side chains and salts thereof;
b) at least one olefinic monomer selected from vinyl compounds selected from the group consisting of aromatic vinyl compounds, vinyl ethers, vinyl esters and nitrogen-containing vinyl compounds, and aliphatic olefins; and
c) at least one hydrophobic compound free of olefinic unsaturation containing units of the formula: 
wherein R1 is independently at each occurrence selected from hydrogen and C1-C4 alkyl, with the proviso that at least one R1 is selected from C1-C4 alkyl in an amount of 0.01 to 30 weight percent, based on the total amount of a), b) and c); at a temperature in the range of 25xc2x0 C. to 100xc2x0 C., and in the presence of a free-radical initiator in an amount of 1.0 weight percent to 25 weight percent, based on the total weight of a), b) and c).
According to a further aspect, the present invention refers to a copolymer containing structural units derived from
a) at least one monomer selected from xcex1,xcex2-unsaturated monocarboxylic acids and their salts; and xcex1,xcex2-unsaturated dicarboxylic acids, their half-esters free of polyalkylene oxide side chains and salts thereof;
b) at least one olefinic monomer selected from aromatic vinyl compounds and aliphatic olefins; and
c) at least one hydrophobic compound free of olefinic unsaturation containing units of the formula: 
wherein R1 is independently at each occurrence selected from hydrogen and C1-C4 alkyl, with the proviso that at least one R1 is selected from C1-C4 alkyl in an amount of 0.01 to 25 weight percent, based on the total amount of a), b) and c), said hydrophobic moiety being incorporated into the copolymer chain, and to the use of these copolymers as plasticizer in cementitious compositions, as well as to a cementitious composition comprising this polymer.
An essential feature of the present invention is that the hydrophobic compound containing at least one oxyalkylene unit wherein alkylene is at least propylene or a higher homologue is incorporated into the copolymer chain formed by the xcex1,xcex2-unsaturated mono- or dicarboxylic acids or derivatives thereof and the olefinic monomer. Incorporated into the copolymer chain means, in the context of the present invention, that the hydrophobic compound is copolymerized with the ethylenically unsaturated comonomers of the present invention via a radical mechanism, thus incorporating the hydrophobic moiety via a carbon/carbon bond into the copolymer chain. The above-discussed structure of the copolymer of the present invention has been confirmed by 13C-NMR and 1H-NMR spectroscopy.
This is in contrast to the disclosure of U.S. Pat. No. 5,661,206 wherein the defoaming agent, although present during the polymerization step, is not grafted onto or incorporated into the polymer chain but rather remains a separate component present in the resulting dispersion. Thus, according to the teaching of U.S. Pat. No. 5,661,206, the purpose of having the hydrophobic defoaming agent present during the polymerization step is to improve the stability of the dispersion of the defoaming agent in the polymer solution.
It is believed that the hydrophobic compound is incorporated (grafted) as an end group or as a side chain into the copolymer backbone forming stable carbon/carbon linkages. It is also believed that, due to the high concentration of initiator, a proton is abstracted from an oxyalkylene unit of the hydrophobic compound wherein oxyalkylene units having secondary carbon atoms, like oxypropylene and higher homologues, are considerably more reactive, thus forming a radical on the hydrophobic compound which then copolymerizes with the olefinic comonomer, preferably styrene. The hydrophobic compound is incorporated into an olefin sequence bearing at the end (as a reactive olefin radical) a growing chain which then, of course, can also react statistically with the xcex1,xcex2-ethylenically unsaturated mono- or dicarboxylic acids or derivatives thereof.
It has been surprisingly found that the presence of olefinic monomers selected from aromatic vinyl compounds and aliphatic olefins is important to achieve the desired incorporation of the hydrophobic compound into the polymer backbone. If such olefinic monomers are not present and only the unsaturated component a), even in combination with other unsaturated monomers, like other acrylic monomers, is polymerized in the presence of component c), the incorporation of the hydrophobic moiety into the polymer backbone does not occur.
Another characteristic feature is that the polymerization is conducted in an aqueous medium, preferably in a mixture containing water and a low boiling alcohol. It is believed that the hydrophobic component c) acts in an aqueous medium in a first step, in particular for the hydrophobic olefinic monomer b), as a kind of emulsifier thereby forming micelies with the monomers present in the polymerization mixture. In a second step, the above-described grafting reaction may occur.
Additionally, it is assumed that the alternative route of forming radicals by abstracting hydrogen from the hydroxy groups does not take place, or if it takes place it is of less importance. This can be confirmed by the fact that the above-described reactions are preferably carried out in an aqueous solvent containing lower alcohol(s). Although the concentration of the alcohol(s) is then considerably higher than the hydroxy-functional hydrophobic compound, incorporation of the alcohol is not detected. Also, the use of polyoxyalkylene glycols having two hydroxy groups as hydrophobic compound does not lead to gelification of the composition.
In contrast to most of the prior art references where hydrophobic compounds, that is, polyoxyalkylene glycol, are incorporated into the copolymer chain via an ester linkage or an amide linkage to an unsaturated mono- or dicarboxylic acid, the hydrophobic compound of the present invention is incorporated into the molecular chain of the copolymer via stable carbon/carbon bonds. It is believed that thereby a very high stability to hydrolysis reactions, especially in basic environments, is achieved. Thus, the copolymers of the present invention are, in contrast to plasticizers wherein the hydrophobic moiety is attached via an ester linkage to the copolymer backbone, less susceptible to hydrolysis reactions and thus the beneficial properties like reduced air entrainment are maintained, even after long storage times especially in a basic environment.
Additionally, it was very surprising, especially in view of the teaching of EP-A-271 435, that the hydrophobic compounds of the present invention can be incorporated via a radical mechanism, although they are only present at a very low level compared to the teaching of EP-A-271 435, wherein the polyoxyalkylene glycol is used in considerable excess, that is, as solvent.
Thus, it is a surprising effect of the present invention that a plasticizer for cementitious compositions can be provided at considerably lower costs by reducing the amount of expensive raw material without compromising the low air entrainment. Furthermore, the plasticizers of the present invention are very stable even during a long storage period.
According to a preferred embodiment of the present invention, the hydrophobic compound to be used in the polymerization process of the present invention is selected from:
c1) polyalkylene oxide compounds corresponding to the formula: 
xe2x80x83wherein R1 is independently at each occurrence selected from hydrogen and C1-C4 alkyl, with the proviso that if ethylene oxide units are present, their content is less than 50 weight percent, based on the total weight of the polyalkylene oxide compound, R2 is selected from hydrogen and from C1-C33 linear or branched, substituted or unsubstituted hydrocarbyls, and m is an integer selected such as to provide a molecular weight of the polyalkylene oxide compound in the range of 500 to 10,000, preferably 1,000 to 8,000;
c2) polyalkylene oxide compounds corresponding to the formula: 
xe2x80x83wherein R1 is independently at each occurrence selected from hydrogen and C1-C4 alkyl, with the proviso that if ethylene oxide units are present, their content is less than 50 weight percent, based on the total weight of the polyalkylene oxide compound, Q is a divalent aromatic group, R2 is selected from hydrogen and from C1-C33 linear or branched, substituted or unsubstituted hydrocarbyls and m and n are integers independently selected to provide a molecular weight of the polyalkylene oxide compound in the range of 500 to 10,000, preferably 1,000 to 8,000;
c3) polyalkylene oxide compounds according to c1) or c2) additionally containing polydiorganosiloxane blocks;
c4) polyalkyiene oxide substituted alkanolamines, wherein the polyalkyleneoxide chain contains units of the formula 
xe2x80x83wherein R1 is independently at each occurrence selected from hydrogen and C1-C4 alkyl, with the proviso that at least one R1 is selected from C1-C4 alkyl and at least one free hydroxyl group and at least one tertiary or secondary amine group is present; and
c5) polydiorganosiloxanes having at least one polyalkylene oxide chain grafted thereon, wherein the polyalkylene oxide chain contains units of the formula 
xe2x80x83wherein R1 is independently at each occurrence selected from hydrogen and C1-C4 alkyl, with the proviso that at least one R1 is selected from C1-C4 alkyl and at least one free hydroxyl group is present in the polydiorganosiloxane.
Preferably, the hydrophobic compound does not contain ethylene oxide units.
Particularly suitable are polyalkylene oxide substituted alkylalkanolamines selected from alkanolamines corresponding to the formula
N(H)a(CH2CH2OT)b(CH2CH2O"Parenopenst"A"Parenclosest"T)3xe2x88x92axe2x88x921
wherein A is a polyalkylene oxide moiety corresponding to the formula: 
xe2x80x83wherein R1 is independently at each occurrence selected from hydrogen and C1-C4 alkyl, with the proviso that if ethylene oxide units are present, their content is less than 50 weight percent, based on the total weight of the polyalkylene oxide moiety, and m is an integer selected to provide a molecular weight of the polyalkylene oxide moiety in the range of 500 to 10,000, preferably 1,000 to 8,000; T is independently at each occurrence selected from hydrogen and a carbonyl moiety of the formula 
wherein R3 is selected from C1-C30 hydrocarbyl, with the proviso that at least one T is hydrogen; and a and b are zero or one.
The most preferred hydrophobic compounds to be used in the process according to the present invention and to be incorporated into the copolymer of the present invention are selected from
(i) poly(ethylene oxide/propylene oxide)glycols, optionally etherified at one terminal position with a C1-C24 alkyl group and containing no more than 50 weight percent, preferably no more than 15 weight percent, ethylene oxide units based on the weight of the hydrophobic compound,
(ii) poly(propylene oxide)glycols, optionally etherified at a terminal position with a C1-C24 alkyl group,
(iii) poly(butylene oxide)glycols, optionally etherified at one terminal position with a C1-C24 alkyl group,
(iv) poly(butylene oxide/propylene oxide)glycols, optionally etherified at one terminal position with a C1-C24 alkyl group,
(v) poly(ethylene oxide/butylene oxide)glycols, optionally etherified at one terminal position with a C1-C24 alkyl group and containing no more than 50 weight percent ethylene oxide units, based on the weight of the hydrophobic compound, and
(vi) poly(ethylene oxide/propylene oxide/butylene oxide)glycols, optionally etherified at one terminal position with a C1-C24 alkyl group and containing no more than 50 weight percent ethylene oxide units, based on the weight of the hydrophobic compound.
Preferably, the hydrophobic compounds of the present invention are long-chain polyalkylene oxides which are known to be effective as defoamers. These compounds are preferably made from propylene oxide or butylene oxide by initiation with an alcohol such as methanol, ethanol, butanot or higher fatty alcohol or mixtures thereof. Preferred are more hydrophobic alcohols such as butanol or higher fatty alcohols. Ethylene oxides can also be used as a comonomer with propylene oxide and/or butylene oxide, however, their level should not be higher than 50 weight percent, based on the total weight of the hydrophobic compound. Examples of the polyalkylene oxide compounds used as hydrophobic compounds of the present invention are: Synalox* 25-50B, Synalox* 25-220B, Synalox* 25-300B, Synalox* 50-15B, Synalox* 50-30B, Synalox* 50-50B, Synalox* 50-100B, Synalox* 50-155B, Synalox* 50-300B, Terralox* OH28, Terralox* OH32 and Terralox* OA32 (*Trademarks of The Dow Chemical Company). These are all ethylene oxide/propylene oxide copolymers with a maximum content of ethylene oxide units of 50 weight percent, based on the weight of the polyalkylene oxide and are commercially available from The Dow Chemical Company.
Suitable propylene oxide polymers for modifying the copolymer of the present invention are the commercial products Synalox 100-20B, Synalox 100-30B, Synalox 100-50B, Synalox 100-85B, Synalox 100-120B, Synalox 100-150B, DowFine 1000 and DF-141, all commercial products obtainable from The Dow Chemical Company.
Examples of butylene oxide polymers suitable to modify the copolymer of the present invention are the commercial products Synalox OA15, Synalox OA25, Synalox OA60, Synalox OA90, and Synalox OA185 commercially available from The Dow Chemical Company.
Other preferred compounds that can be used to modify the copolymer of the present invention are derivatives of polyalkylene oxide polymers corresponding to the formula 
wherein EO, PO, BO represent randomly arranged ethylene oxide, propylene oxide and butylene oxide units, respectively, u, v, and w are integers from 0 to 50, with the proviso, that no more than 50 weight percent ethylene oxide units, based on the weight of R, are present and r is 0 to 35. These compounds are also commercially available from The Dow Chemical Company under the Trademark Dowfax, such as, for example Dowfax* D141 (*Trademark of The Dow Chemical Company).
These polyalkylene oxide compounds are particularly preferred since they result in copolymers according to the present invention that, if used as cement plasticizers, result in the reduction of an air entrainment in cement, mortar, and concrete.
The xcex1,xcex2-unsaturated monocarboxylic acids and salts thereof to be used as component a) for preparing the copolymer of the present invention are preferably selected from acrylic acid, methacrylic acid, crotonic acid and itaconic acid. Suitable xcex1,xcex2-unsaturated carboxylic acids are selected from maleic acid and fumaric acid, as well as their half-esters and salts thereof. The olefinic component b) is preferably selected from styrene, xcex1-methylstyrene, ethylene, propylene, isobutylene, diisobutylene, 1-butene, 1-octene, vinyl ethers, vinyl esters, acrylonitrile, acrylamides and vinylpyrrolidone, wherein styrene is the most preferred olefinic component according to the present invention.
According to a second preferred embodiment of the present invention, at least one ethylenically unsaturated monomer d) containing polyalkylene oxide side chains is co-polymerized with components a), b) and c) as discussed above. It has been surprisingly found that the resulting copolymers are cement additives that do not, or only to a reasonable extent, retard the setting of the cement without compromising the advantageous long-term air entrainment properties of the copolymers of the present invention.
The unsaturated monomers containing the polyalkylene oxide side chains are preferably derivatives of unsaturated mono- or dicarboxylic acids such asxe2x80x94alkoxypolyalkylene glycol mono(meth)acrylates, half-esters or di-esters obtainable by reacting maleic anhydride with polyalkylene glycol monoethers, and half-amides obtainable by reacting maleic anhydride with polyalkylene oxide substituted alkanolamines, or adducts of allyl alcohol and alkylene oxides, and adducts of (meth)acrylamide and alkylene oxides. The number of alkylene oxide units in the monomer d) is preferably 3 to 300. These monomers contain preferably pure ethylene oxide structural units, but propylene oxide and butylene oxide and mixtures thereof may be additionally present. Preferably, their content is less than 25 weight percent, more preferably less than 10 weight percent, based on the total amount of alkylene oxide units. The most preferred monomers d) are methoxypolyethylene glycol mono-(meth)acrylates having from 7 to 30 ethylene oxide units per molecule. Mixtures of methoxypolyethylene glycol mono- (meth)acrylates with different numbers of ethylene oxide units can also be advantageously used.
According to the present invention, the hydrophobic compound is present in an amount of 0.01 to 30 weight percent in the reaction composition, based on the total weight of the monomers. Preferably, the amount of hydrophobic component c) is 0.5 to 20 weight percent, most preferably 5 to 15 weight percent, based on the total weight of monomers present. The weight ratio of monomers a:b, in case component d) is absent, is preferably within the range from 10:90 to 90:10, more preferably from 30:70 to 70:30, and most preferably about 50:50. In case component d) is present, component a) preferably is present in an amount of 0.5 to 40 weight percent, component b) preferably is present in an amount of 0.5 to 50 weight percent and component d) is present in an amount of 10 to 99 weight percent, based on the total weight of component a), b) and d).
The process according to the present invention is preferably performed in an aqueous solvent comprising an alcohol having a boiling point below 100xc2x0 C.
The weight ratio alcohol/water is preferably 1:5 to 5:1, more preferably 1:3 to 3:1, and most preferably 1:2 to 2:1. Preferred alcohols are methanol, ethanol, propanol or isopropanol, but other low boiling alcohols may also be used. The most preferred low boiling alcohol is isopropanol.
The hydrophobic compound is preferably added to the alcohol/water/ethylenically unsaturated monomer mixture before the polymerization is started, that is, before the initiator is added. Also possible, but less preferred, is the continuous or portion-wise addition of the hydrophobic compound during the course of the polymerization, either separately or in a mixture with the monomer or the initiator stream.
Initiators for the free radical polymerization reactions are preferably inorganic peroxides, like peroxydisulfates such as ammonium, sodium or potassium peroxydisulfate or hydrogen peroxide and mixtures thereof. These peroxides can also be used in combination with redox-co-catalysts such as heavy metal salts, that is, Fe salts, sulfur compounds, that is, NaHS, amines or hypophosphites in order to promote their decomposition rate. In particular, if hydrogen peroxide is selected, Fe salts are advantageously used.
The use of organoperoxides such as benzoyl peroxide or azo-initiators such as azoisobutyronitrile or water-soluble azo-initiators is possible, but less preferred. For example, if azo-initiators are used, it is preferred to utilize the olefinic component b) in an amount of at least 15 weight percent, more preferred at least 20 weight percent, based on the total amount of ethylenically unsaturated monomers. Surprisingly, it has been found that a higher level of initiator than commonly used in the case of a free radical polymerization has to be used in order to enable the grafting of polyether onto the copolymer backbone. The initiator is used at the level of from 1.0 weight percent to 25 weight percent, based on the weight of the monomers, preferably in an amount of from 2.5 to 20 weight percent, most preferably 5 to 15 weight percent. If co-initiators are used, the initiator/co-initiator mole ratio can be from 1:10 to 10:1, preferably, however, the mole ratio is 1:1. In this case, the initiator level is usually somewhat lower and can be from 1 to 20 weight percent, preferably from 3 to 20 weight percent, depending on the kind of co-initiator and the polymerization conditions such as temperature applied. Preferably, no co-initiator is used, except in the case of hydrogen peroxide.
In addition, chain transfer agents to control the molecular weights of the graft copolymer can be present and include dodecylmercaptane or allyl derivatives.
The polymerization temperature is in the range of 25 to 100xc2x0 C., preferably from 40 to 90xc2x0 C., and most preferred in the range of 60 to 85xc2x0 C. The polymerization reaction times are between 0.2 to 10 hours, preferably between 0.5 and 8 hours, most preferably from 1 to 5 hours depending on the polymerization temperature.
The low boiling alcohol is distilled from the reaction mixture after polymerization and can be recycled. Prior to distillation, the polymer can be partially or completely neutralized with diluted caustic. Instead of caustic amines such as triethanolamine or derivatives prepared from triethanolamine by conversion with propylene, ethylene or butylene oxides having one terminal amine function can be used. Ammonia solutions are less preferred. The neutralization can be conducted in such a way that caustic is added simultaneously under reflux conditions while removing the alcohol/water mixture either under vacuum or under normal pressure conditions. Preferred is, however, a process by which the neutralization is mainly performed after the removal of the alcohol/water mixture.
Although an alcohol/water mixture is most preferred, in some cases the alcohol can be replaced with an ester or ketone such as methyl or ethyl acetate or acetone. The ester and/or ketone should preferably be miscible with water and the boiling point should be below 100xc2x0 C. However, as stated, an alcohol is most preferred due to its chemical stability under the reaction process conditions applied.
If an unsaturated monomer containing polyalkylene oxide chains according to component d) is used, the polymerization can also be conducted in water as the sole solvent since monomers of component d) are sufficiently water-soluble or water-dispersible and additionally enhance the dispersibility of the olefinic component. However, even if component d) is present, an alcohol/water mixture is the preferred reaction medium.
The molecular weight of the grafted copolymers are in general from 1,000 to 100,000, preferably from 3,000 to 60,000, and most preferably from 5,000 to 30,000, based on the weight average molecular weight (Mw).
The copolymers of the present invention can be used as additives, such as plasticizer, for cementitious compositions, especially those that are used for construction purposes, to increase the flowability of the cementitious composition. Especially preferred is the use of the copolymers of the present invention in mortar and cement compositions.
Thus, according to a further aspect, the present invention refers also to a cementitious composition comprising the copolymer of the present invention. These cementitious compositions for construction purposes, like mortar or cement, usually comprise a hydraulic binder, aggregate and water. According to a preferred embodiment, the copolymer of the present invention is present in these cementitious compositions in an amount of 0.001 to 2.5 weight percent, preferably 0.01 to 0.1 weight percent, based on the weight of the hydraulic binder. Preferably, the copolymer of the present invention is added to the cementitious composition in form of an aqueous solution/dispersion (concentrate) containing the copolymer in a concentration of 5 to 50 weight percent, preferably 15 to 35 weight percent.
The cementitious composition of the present invention may contain other usual additives, for instance aluminum salts like aluminum sulfate, aluminum hydroxide or aluminum hydroxysulfate as accelerators for the setting of the concrete. These and other usual additives may be either incorporated into the concentrate of the copolymer of the present invention or may be added directly to the cementitious composition.
Besides the effect of reducing the foam level in the cementitious composition, the copolymers of the present invention impart additional advantageous properties to the cementitious compositions. For example, it is known that defoamers can be added to solutions of the non-modified polymers of the prior art to reduce the high foam level of these solutions. However, all known defoaming systems tested so far, separate from the aqueous polymer solution in a couple of days and, thus, their performance is lost and the solutions exhibit the high initial foam level again. Surprisingly, it has been found that, if defoamers are added to the aqueous solutions/dispersions of the copolymers of the present invention, they do not separate even after a prolonged period of time.
The following examples are provided to illustrate the present invention in more detail and should not be construed as limiting its scope. Unless otherwise indicated, all parts and percentages are by weight.